Process for producing coated elements



Jan. 15, 1935. J E. SMITH PROCESS FOR PRODUCING COATED ELEMENTS Filed July 28, 1931 M iQC 11 latented Jan. 15, 1935 UNITED STATES PATENT OFFICE PROCESS FOR PRODUCING COATED LEMENTS of Missouri Application July 28, 1931, Serial No. 553,571

1 Claim. (Cl. 201-67) The present invention relates to the process of producing metallic or other solid materials coated with an argillous material.

The invention in its broadest aspect is applicable to the coating of materials generally such as wood, metals, tiles, etc., with a coating of argillous material. More especially, the process is intended for the coating of metals, and more particularly for the coating of electrical resistance elements with an argillous insulating material. The foregoing reference to metals includes plates, strips, screens or grids, and wires. The following description will be carried out with reference to electrical resistance elements only, by way of example.

The argillous material is somewhat in the nature of a ceramic material. Whether dry or a plastic, moist substance made from granular material into a suitable body or paste, with suitable moistening and binding mediums, it is subsequently intended to be hardened by the application of heat.

Processes have been heretofor proposed to imbedelectrical resistance elements in certain 5 granular materials intended to insulate the elements and at the same time withstand the high temperatures to which such elements are subjected. The insulating material may be either dry in powdered form, or mixed with a moistening element.

Such processeshave, however, required the application of very high pressures and the use of special dies to withstand such pressures and to retain the element during its entire manufacturing process, namely, through the steps of imbedding the element, its sheathing, and its subsequent baking and curing. Consequently, to reach any quantity production with such a process has involved a very substantial money outlay for the special machinery and equipment required.

The prior processes are practiced by inserting the element into the insulating material and compacting the insulation about the resistor ele- 45 ment. Therefore, by such process, the elements are not coated with the insulating material in the sense of applying to the element a covering that adheres or clings to it. The former is an imbedding of the element, the latter is 50 coating the element in much the same sense as coating a wall with paint. It is one object of my invention to provide a process of coating any solid element with an argillous or ceramic material.

It is another object of my invention to provide a process whereby an element may be coated with an argillous or ceramic material by the application of pressures of a minor order, and with or without the presence of heat.

It is still another object of my invention to provide a process of coating an electrical resistor element with an argillous insulating material.

It is a further object of my invention to provide a process of coating an element of any character with an argillous material which consists in extruding the element and the material from a holder.

It is a further object of my invention to provide a process for coating an electrical resistor element to thereby produce a coated element which is of suflicient tenacity that it may be wound around or formed into any desired shape for its future use with layers of the coated ele-' ment touching or not as desired.

It is a still further object of my invention to provide a process for producing an insulated electrical resistance element of the above indicated character that may be used in service with or without a sheathing or case.

It is a still further object of my invention to provide a process of coating a coiled wire which consists in applying a coating of argillous material so as to tend to spread the turns of the coil to permit the entrance of the material between the turns.

It is an even further object of my invention to provide a process of coating a coiled wire which consists in applying the coating of argillous material both on the exterior and the interior of the coil.

It is an even further object of my invention to provide a process of forming a tubular heating element which consists in filling the inside of a tubular case with a resistance wire coated with an argillous material, the pressure of applying the coating being utilized to insert the coated wire into the tube.

Other and further. objects of my invention will be apparent from the following specification taken in conjunction. with the accompanying drawing, wherein- Figure 1 is a vertical section of one form of machine for carrying out my improved process;

Fig. 2 is a detail of the connection permitting the removal of the piston; and

Fig. 3 is another detail showing the key and slot arrangement for the piston operating shaft.

In practicing my process of coating electrical heating elements with an insulator, the argillous material may be mixed and formed into a plastic body or paste ready to be applied to the heating elements. Since the making of this mixture forms no part of the invention claimed herein, it will not be further defined here except to state that a satisfactory composition for this purpose includes an aluminum oxide, or the like, base with a moistening agent (where the paste or plastic form is used), and an appropriate binder.

A cartridge of the body or paste is then introduced into a machine into which is also introduced the heating element that is to be coated. Pressure is then applied to the cartridge so-as to extrude the plastic body from the machine through a nozzle, provided for that purpose. The element to be coated is introduced into the nozzle and is ejected from the machine by the same force and the same action that extrudes the plastic material from the machine. As the element and the plastic material emerge from the machine, the plastic material is coated upon the element and clings thereto. The coated element may then be wound or shaped into any form desired, and the contiguous layers of the coated element may touch each other without danger of damaging the electrical resistor element or of damaging the coated element. The element is then baked so as to dry the same and harden it. The element may or may not be introduced into a casing or sheathing.

No further reference will be made herein to the formation of a shaped heating element, this being more specifically referred to and claimed in copending applications directed thereto.

The operation of my process will be best understood by reference to the accompanying drawing which is illustrative of the operation of a machine for carrying out my process.

The machine comprises a cylinder 1 having screwed thereupon a head 2 which is tapered to a reduced discharge mouth 3. The mouth 3 is provided with an annular shoulder 4 against the outside of which rests the rear end of a removable nozzle 5. The nozzle 5 has a shoulder 6 extending beyond the rim '7 of the mouth 3 which shoulder is engaged by a cap 8 that screws upon the rim '7 so as to secure the nozzle 5 firmly in the mouth 3.

A plunger or piston 11 is adapted to be moved back and forth in the cylinder 1. The connecting rod 12 that is attached to the piston head 11 has a sleeve 13 secured thereto by means of a bayonet and slot connection 14 shown in detail in Fig. 2. On the opposite end the sleeve 13 is secured to a hollow shaft 15 which is externally screw threaded as indicated at 16. Cooperating with the screw threaded portion of shaft 15 is a nut 17 which nut forms part of the hub of a bevel gear 18. A second bevel gear 19 cooperates with the bevel gear 18 and has a shaft 20 which is connected to a source of power (not shown) in any appropriate manner. The bevel gears are securely mounted in a housing 21 which is held in position with respect to head 2 by means of a plurality of spacer rods 22. The shaft 15 is provided with a key way or slot with which key 23 cooperates to prevent the shaft from turning as the gears 18 and 19 rotate. The key 23 is integral with plate 24 forming part of the housing 21.

It will be obvious from this simple assembly that when power is applied to the shaft 20 to turn the bevel gear 19, the bevel gear 18 will be rotated which will rotate the nut 17 causing the shaft 16 and the connected piston head 11 to travel inwardly or outwardly according to the direction of rotation of the gears.

The following is the procedure when loading the machine:

The piston 11 is withdrawn in the cylinder 1 as far as possible by operation of the screw 16. The bayonet joint 14 between the sleeve 13 and piston rod 12 is unlocked and the rod 12 is telescoped into the sleeve 14 so as to remove the piston from the cylinder as shown in the dotted line position in Fig. 1. A cartridge of my plastic or argillous coating material is then introduced into the cylinder.

After the cartridge is introduced, the-piston head is inserted in the cylinder 1 and the bayonet joint 14 is relocked. Further movement of the piston head 11 by rotation of the driving nut 17 will exert pressure upon the cartridge which will compress the same downwardly in the cylinder toward the head 2. The beveled inner surface of the head 2 will direct the material toward the discharge mouth 3 and the nozzle 5 mounted therein. Further pressure will force or extrude the material 3 through the opening in the nozzle 5.

The resistor element that is to be coated is introduced into the machine and rests in a tubular carrier 31 which extends through a central bore in the piston, the piston rod 12, the sleeve 13 and the hollow shaft 15 projecting beyond the end of the shaft 15 as shown at the upper end of Fig. 1. The inner end of the tube 31 is maintained centrally disposed in the head 2 by means of a spider wheel 32 that is locked between the cylinder 1 and head 2, the end of the tube 31 being maintained spaced from the inner end of the nozzle 5, which permits the passage of the argillous material into the nozzle 5 as described above. The resistance element is indicated at 33 as a coiled wire which extends beyond the tube 31 and through the bore of the nozzle 5. The wire may be fed from a continuous supply (not shown) located outside of the machine as shown in the drawing.

As further pressure is exerted upon the cartridge of plastic material and the material is extruded through the bore of the nozzle 5, the pressure and force necessary to extrude the material forces it upon and applies it to the element 33 both in the space between the inner end of the tube 31 and the inner end of the nozzle 5, and also in the bore of the nozzle 5. Likewise, this same pressure that is used to extrude the plastic material from the nozzle 5 is sufficient to carry the coated element out of the machine. It is apparent that so long as this pressure continues forcing the piston head 11 inward, and there is sufficient plastic material in the cylinder 1, the resistance element will be coated and also ejected or extruded from the nozzle 5 in a continuous flow.

A coiled resistance element 33 is shown in the drawing to illustrate a further feature of my invention in the use of a tapered head 2. The pressure which is exerted upon the material and the element 33 in the space between the inner end of the tube 31 and the inner end of the nozzle 5 is approximately in thedirection of the tapered or conical surface of the head. This pressure in this direction is of such a nature as to cause a tendency of the turns of the coil 33 to spread apart sufficiently to insure that the turns do not touchand therefore become shortcircuited. The spreading apart or spacing is also suflicient to permit the entrance of the argillous material between the turns and into the interior of the coil thereby illling the interior of the coil and remaining between the turns of the coil thereby insulating the turns from each other, in addition to coating the outside of the wire.

It is apparent from the foregoing that the resistance element 33 herein is coated in the true sense of the word by having the argillous material applied thereto. It is of such. a nature that it clings to the resistance element and when the coated element is subsequently heated and dried out, the coating becomes hard and the element is permanently coated. In the case'of an electrical resistance element, the argillous material is naturally composed of electrical insulating materials capable of withstanding the high temperatures to which such elements are subjected, and in use the whole element glows.

This same process of coating a resistance element with argillous material applies equally well whether the element being coated is of wire, or a strip of metal, or a grid, or a plate.

The same process is applicable whether the element is metal, wood or other material. Likewise, the composition of the argillous material may be varied in accordance with the varying uses to which the finished article is to be put.

As illustrative of a method of sheathing the coated resistor element as described above. there is indicated in dash lines a tube 34 at the discharge end of the nozzle 5. As the coated ele-' ment is extruded from the noule it directly into the end of the tube 34, and the extrusion pressure upon the coated material is suflicient to force the coated element into and along the tube or sheathing 34 thereby filling the same. If the sheathing 34 is flexible, then this sheathed coated element may be formed and twisted into any shape desired as described above, and the layers of the sheathing may contact each other without danger of short circuit.

Varying sizes and shapes of elements may be obtained by changing the nozzles 5, each having a difierent bore.

In carrying out the foregoing process it will be noted that there has been no reference made to the of heat until the coated element is baked or cured after completion. That is correct for some elements, but in others it may be more desirable to apply heat at the machine during the extrusion of the coated element. Likewise, for some elements the cylinder may be filled with powdered or granular material made into an adhering coating by chemical action or the action of heat and which will still leave the element flexible enough to be shaped in the form desired for permanent use or mounting.

It is further apparent that forces necessary to extrude the argillous material from a discharge mouth are of a minor order, especially as compared to pressures necessary to imbed a resistance in a granular material and compacting the material to insure the necessary insulation.

Other modifications may be made in the steps of my process that are within the spirit and scope of my invention, and such modifications are intended to be covered by the appended claim.

I claim:

The process of producing a coated coiled resistance element which consists in simultaneously extruding argillous material and a coiled resistance element from a holder with the argillous material being extruded around and within the coiled resistance element and both being extruded into a containing casing.

JOHN E. SMITH. 

